Bug 218840 add some null checks that were preventing autocomplete from working in message compose r=timeless sr=mscott

xpfe/components/autocomplete/resources/content/autocomplete.xml

@@ -584,7 +584,8 @@
           }
           
           if (firstReturn) {
-            this.view.mTree.beginUpdateBatch();
+            if (this.view.mTree)
+              this.view.mTree.beginUpdateBatch();
             this.clearResults(false); // clear results, but don't repaint yet
           }
           this.mLastResults[aSessionName] = aResults;
@@ -597,7 +598,7 @@
           // be sure to add our result elements before calling openResultPopuup as we need
           // to know the total # of results found so far.
           this.addResultElements(aSessionName, aResults);      
-          if (firstReturn)
+          if (firstReturn && this.view.mTree)
             this.view.mTree.endUpdateBatch();
           this.openResultPopup();